45 rpm means 45 revolutions per minute, and have a larger hole, in the center.
33 rpm = 33 revs per minute, etc, and use a smaller hole.

the smaller 7" "singles" are usually 45 rpm, (except for a few "EP’s" which are 33 rpm)
the larger 12" are 33 rpm.
78 rpm, hasn’t been used since the ’50’s you aren’t going to see many of them.

33 and 45 will cover 99.9 % of the records out there, unless you are specifically looking for old 78’s.

It’s not really about which is better, it’s about "matching" the record and the player,
You have to play the record at the same speed it was recorded at.
Most players will play 45’s and 33’s, tho you might need an "adapter" to play 45’s, if the player just has the 33" "spindle"

You will need an amp or preamp, that has a "phono" input, for them to sound right.
the music industry rolls some of the bass off, when they are pressed, so that the needle doesn’t move around too much,
It’s known as the RIAA EQ curve.